Problem: Umaima is 4 times as old as Kevin and is also 30 years older than Kevin. How old is Kevin?
Answer: We can use the given information to write down two equations that describe the ages of Umaima and Kevin. Let Umaima's current age be $u$ and Kevin's current age be $k$ $u = 4k$ $u = k + 30$ Now we have two independent equations, and we can solve for our two unknowns. Since we are looking for $k$ , and both of our equations have $u$ alone on one side, this is a convenient time to use elimination. Subtracting the second equation from the first equation, we get: $0 =$ $4k$ $-$ $ (k + 30)$ which combines the information about $k$ from both of our original equations. Solving for $k$ , we get: $3 k = 30$ $k = 10$.